Editorial Slides VP Watch, December 31, 2001, Volume 1, Issue 39

MRI Scanner; Should Cardiologists Have One?!

The first successful nuclear magnetic resonance (NMR) experiment was made in 1946 independently by two scientists in the United States. Felix Bloch, working at Stanford University, and Edward Purcell, from Harvard University, found that when certain nuclei were placed in a magnetic field they absorbed energy in the radiofrequency range of the electromagnetic spectrum, and re-emitted this energy when the nuclei transferred to their original state. For this discovery Bloch and Purcell were awarded the Nobel Prize for Physics in 1952.1

Evolution of the above discovery to magnetic resonance imaging (MRI) as the most powerful non-invasive clinical diagnostic tool, is best owed to many scientists world wide.1

In the past two decades, MRI has been slowly introduced into the world of cardiovascular medicine.

In early 1980s Higgins and others envisioned MRI applications for detection of cardiac structural abnormalities (such as congenital anomalies) as well as acute and remote myocardial infarctions, atherosclerotic plaques, hypertrophic cardiomyopathy, pericardial diseases, aneurysms, and patency of bypass graft. They also suggested that diagnostic utility of MRI includes direct tissue characterization, and such utility may be further extended by the use of paramagnetic contrast media. 2

In 1991, Manning et al. demonstrated the power of noninvasive MRI coronary angiography to identify substantial stenosis correctly within the proximal portion of major coronary arteries in a group of patients undergoing conventional contrast coronary angiography. Other investigators also introduced MRI application in non-invasive coronary imaging.3,4,5

In 1993, Manning et al. showed that single breath-hold MR coronary angiography provides visualization of the major epicardial vessels, suggesting MR coronary angiography may provide a noninvasive means for the evaluation of patients with known or suspected coronary artery disease.6

Despite the feasibility studies shown by Manning and others years ago, the idea of non-invasive coronary angiography by MRI has not been clinically adapted.

However, several other novel clinical applications for MRI in cardiovascular medicine have rapidly developed in the recent years. (see next table)

Similar rapid progress in cardiovascular imaging has been accomplished through other imaging modalities, in particular CT.

Adapted from: Philips Medical System, Intera CV, 2001

As highlighted in this week of VP Watch, Manning et al. reported non-invasive coronary MRA as a new clinically available tool for screening coronary artery stenosis (particularly left main and 3-vessel) among high risk patients.7

They found that the sensitivity, specificity, and accuracy of MRA for patients with stenotic disease of the left main coronary artery or 3-vessel disease were 100% (95% confidence interval, 97-100%), 85% (95% confidence interval, 78-92%), and 87% (95% confidence interval, 81-93%), respectively.7

Overall, coronary magnetic resonance angiography had an accuracy of 72% (95% confidence interval, 63-81%) in diagnosing coronary artery disease.7

The sensitivity, specificity, and accuracy for patients with disease of the left main coronary artery or 3-vessel disease were 100% (95% confidence interval, 97-100%), 85% (78-92%), and 87% (81-93%), respectively.7

The negative predictive values for any coronary artery disease and for left main artery or 3-vessel disease were 81% (95% confidence interval, 73-89 %) and 100% (95% confidence interval, 97-100%), respectively.7

Conclusion:I. Coronary MRA has shown significant accuracy for

detection of luminal stenosis in proximal portions of epicardial arteries with profound negative predictive value.

II. The publication of Manning et al in The New England Journal of Medicine this week can open the road to widespread use of MRI as a reliable clinical tool available to cardiologists for non-invasive diagnosis of coronary artery stenosis in selected patients.

Questions:1- The long-waiting dream of a non-invasive

angiography technique for accurate diagnosis of coronary stenosis seems to be close to cardiologists’ hands, the question is how well this tool can identify angiographically invisible vulnerable plaques.

2- Although coronary stenosis is a surrogate marker of vulnerable plaques and vulnerability of coronary arteries, between MR angiography and MR plaque characterization which one seems to be more important for diagnosis of vulnerable patients?

Questions:3- CT (MSCT and EBCT) is expected to offer similar

clinical tool for non-invasive coronary angiography most likely at lower cost and faster technique, what would be the advantage of coronary MRA over CT MRA?

4- Should cardiologists buy cardiac MRI scanner, wait for cardiac CT scanner, or send Dx request to radiologists?!

Suggestion:VP.org Editorial Suggestion:

- In addition to non-imaging screening tools, develop a novel composite CHD risk score for coronary imaging diagnostic tools combining luminal narrowing, wall (plaque) vulnerability, and heamodynamic factors.

- MRI and CT industries are suggested to provide more easily reproducible and most automated imaging techniques (software) to allow widespread clinical application of these emerging technologies.

Please email your thoughts to:Discussion-Group@VP.org or DG@VP.org

1. Imaging Science and Biomedical Engineering, University of Manchester; History of MRI: http://www.isbe.man.ac.uk

2. McNamara MT, Higgins CB.; Cardiovascular applications of magnetic resonance imaging.Magn Reson Imaging. 1984;2(3):167-83.

3. Manning WJ, Li W, Edelman RR. A preliminary report comparing magnetic resonance coronary angiography with conventional angiography. N Engl J Med 1993;328:828-832.

4. Manning WJ, Atkinson DJ, Grossman W, Paulin S, Edelman RR.; First-pass nuclear magnetic resonance imaging studies using gadolinium-DTPA in patients with coronary artery disease. J Am Coll Cardiol. 1991 Oct;18(4):959-65.

5. Burstein D; MR imaging of coronary artery flow in isolated and in vivo hearts. J Magn Reson Imaging. 1991 May-Jun;1(3):337-46.

6. Manning WJ, Li W, Boyle NG, Edelman RR. Fat-suppressed breath-hold magnetic resonance coronary angiography. Circulation. 1993 Jan;87(1):94-104.

7. W. Yong Kim, M.D., Ph.D., Peter G. Danias, M.D., Ph.D., Matthias Stuber, Ph.D., Scott D. Flamm, M.D., Sven Plein, M.D., Eike Nagel, M.D., Susan E. Langerak, M.Sc., Oliver M. Weber, Ph.D., Erik M. Pedersen, M.D., Ph.D., Matthias Schmidt, M.D., René M. Botnar, Ph.D., and Warren J. Manning, M.D. Coronary Magnetic Resonance Angiography for the Detection of Coronary Stenose; New England Journal of Medicine 2001; 345(26):1863-1869

References

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Courtesy of Dr. Chun YuanUniversity of Washington